[Optimization of dose distribution in combined irradiation of uterine cervix cancer with gamma-ray cesium-137 and X-9 MeV].

UNLABELLED

This study concerns the optimization of the dose distribution in all variants of combined irradiation of uterine cervix cancer which are used in our Clinic (Tab. 1). The analysis of the doses of radiation in reference points as well as isodose distribution in the whole irradiated area has been done. All variants of combined irradiation and the localization of applicators in the intracavitary irradiation and field's arrangement of external beam irradiation have been shown. The second part of the study analyzes the physical parameters in conventional intracavitary irradiation by modified Manchester method in comparison with the Selectron-LDR (Tab. 5). The dose distribution around the applicators has been compared too. The biological equivalence of the doses in application of different dose rate sources has been estimated according to the principles of LQ-model (Tab. 3, 4). Relations between the reference point doses and such parameters as the length of intrauterine sond (Fig. 2), the size of applied ovoids (Fig. 3), the distance between them (Fig. 5) and the treatment sources' positions in the ovoids (Fig. 4) have been calculated. The dose distribution in all variants of combined irradiation of uteri cervix cancer has been demonstrated (Fig. 6). Total absorbed dose in the point A, as well as in the reference points of bladder, rectum and para-aortic, external iliac and common iliac lymph nodes have been calculated (Tab. 5). The position of regional lymph nodes was defined with the use of lymphography, two orthogonal radiograms and CT. In the last part of the work, after optimization of physical irradiation parameters and their biological equivalents, the dose distribution in all variants of combined irradiation has been calculated (Fig. 7).

CONCLUSIONS

1. The LQ-model allows to calculate the biological equivalent of total physical dose in combined irradiation when intracavitary irradiation is realised with different dose rate sources, and external beam therapy with different doses per fraction. 2. The use of the smallest ovoids in intracavitary irradiation leads to increased dose in the bladder and rectum. The use of small ovoids increases the dose only in the bladder in comparison to utilisation of medium and large ovoids. In such cases individual treatment planning is necessary. 3. The external iliac nodes are located above the points defined in the Fletcher lymphatic trapezoid. Therefore the lateral fields of pelvis lymph nodes irradiation should be at least 10 cm wide. 4. Depending on clinical advancement of uterine cervix cancer the optimisation of combined irradiation allows to obtain the desired dose in the target volume as well as in regional lymph nodes in each variant of irradiation.